The utilisation of electrodes of cylindrical geometry is known in several sectors of electrochemistry. Cylindrical electrodes, in the majority of cases concentrically disposed inside hollow cylindrical counter-electrodes, are currently employed in electrodialysis, water electrolysis, ozone production, and other applications. The most important processes making use of cylindrical-type, mostly coaxial, electrodic geometries are for the recovery of metals from aqueous solutions and the treatment of waste water (industrial wastes, civil waters and others), for the potabilisation or purification thereof from various contaminants. The cylindrical geometries, especially on small-size electrochemical cells, offer substantial advantages particularly in terms of fluid distribution. Depending on the process under consideration, the cylindrical electrodes can be both anodes or cathodes. In the majority of cases, such electrodes are suitable for gas evolution reactions, for instance hydrogen cathodic evolution or oxygen, ozone or chlorine anodic evolution. The gas-evolving reactions, in particular the anodic ones, must be catalysed in order to take place with a sufficient efficiency. The cylindrical electrodes of the prior art, therefore, consist of a metal cylindrical conductive support (usually titanium or other valve metal, in the case of anodes) coated with catalysts usually based on metal oxides, depending on the type of the gas to be evolved and of the required potential, as widely known. The application process of the catalytic coating to the cylindrical support provides painting the latter with a precursor, and the subsequent conversion of the precursor by means of a high temperature thermal treatment (350-700° C.). The painting of metallic electrodes with precursor solutions is preferably carried out by electrostatic spraying processes. The cylindrical geometry is, in this case, less favourable than the planar one in terms of homogeneity of application. Furthermore, the catalytic coatings have a limited operative lifetime (indicatively 1 to 5 years depending on the applications). Once the original coating is exhausted, it must be completely removed by mechanical means and restored. The coating removal operation is particularly onerous for cylindrical geometries, especially for those of small size. In any case, the prolonged times required for restoring the catalytic activity of the electrodes lead to undesirable limitations to the plant operation, alternatively imposing a temporary interruption of the production, an oversize of the whole plant to allow a planned cyclic electrode reactivation, or the need of storing a remarkable amount of replacement electrodes, which is a very onerous solution from the investment cost standpoint.
It would be desirable, therefore, to provide a cylindrical electrode for electrochemical processes overcoming the limitations of the prior art. It would be further desirable to provide a cylindrical electrode allowing an increased easiness of application or of restoring of the catalytic coating. It would be still further desirable to provide an improved method for the catalytic reactivation of a cylindrical electrode in terms of process management efficiency.